Heat exchanger



w. w. KRAFT HEAT EXGHANGER Filed July 51, 1941 W INVENTORWK W ATTORNPatented July 6, 1943 stain NT QE HQE.

HEAT EXCHANGER Wheaton W. Kraft, Scarsdale, N. Y., assignor to TheLummus Company, New York, N. Y., a corporation of Delaware ApplicationJuly 31, 1941, Serial No. 404,861

6 Claims.

This invention relates to improvements in heat exchange apparatus andmore particularly to apparatus for the condensation of hydrocarbonvapors from a distillation process or the like.

As is well known, distillation, particularly fractional distillation, isaccomplished by introducing a hot liquid into a suitable fractionatingcolumnthat may be provided with bubble decks, in which column thevaporous or low boiling portion of the heated liquid risescountercurrently to descending reflux liquid and the higher boilingliquid portion of the charge passes to the lower part of the column. Atvarious points in such a column, portions of the material may be removedas side streams, and such streams are customarily cooled before furthertreatment or storage.

The overhead stream in most distillation processes is a vapor, a largeproportion of which is condensible. To provide for simple handling ofsuch a stream, it is customary to condense it. Some of the resultingcondensate is customarily returned to the column as reflux, and theremainder may be withdrawn as a product.

Particularly in connection with the refining of petroleum, condensationis provided for the overhead streams, and cooling is provided for theside Streams whether they come from the topping unit, the bubble tower,or the stabilizer. Ordinarily, the equipment for condensing the vaporsis designed to discharge a liquid; and, if the cooling medium is notsufficiently available, the large volumes of uncondensed vapors areextremely difficult to handle and usually blow through relief valvestothe atmosphere. In such case, not only are valuable products lost, butthe vapors which escape because of lack of condensation are usuallydangerous from the fire hazard standpoint.

I-Ieretofore, it has been usually found necessary for absolute safety tohave a reservoir of cooling medium such asis provided in a submergedcondenser, which consists of a coil of tubing placed in a large waterbox through which cooling water is, slowly circulated. In suchapparatus, the vapors pass through the coil, and the operation isentirely safe because of the reservoir of water; but the heat exchangeefliciency is low because of the extremely low velocity of movement ofthe cooling water.

In the alternative, the condensing of vapors may, in some cases .becarried out in shell and tube type heat exchangers with. the water inthe tubes and witha resulting high efficiency of heat transfer. In suchcase, however, the operationis completely dependent on a continuance ofthe water supply, an interruption of which may result in disasterbecause of the almost instantaneous failure of the condensing actionwith a resulting blow-through of the vapors.

In accordance with the disclosure of J acocks in his co-pendingapplication for U. S. Patent, S. N. 220,620, filed July 22, 1938, now U.S. Patent 2,254,070, patented August 26, 1941, a heat exchangeconstruction is provided that includes a tank acting as a reservoir forwater which is available during emergencies such as are caused by thefailure of the normal cooling water supply. In such construction, thenormal operation is that of a shell and tube unit having a high heattransfer efiiciency with the water in the tubes; and the residual watersupply may be, for example, approximately equivalent to a thirty minuterequirement in case of a failure of the cooling water. In such a period,it is usualli possible to accomplish a complete shut-down of therefinery unit from which the vapors must be condensed.

The principal object of my present invention is to provide an improvedcondenser for the vapors of a distillation process, in which condenserthe high eificiency of heat exchange afforded by the shell and tubeconstruction is available during normal operations and a high timefactor of safety is afforded in case of accidental failure of thecooling water supply.

More specifically, I provide a condenser apparatus which is adapted tocondense independent vapor streams so that various conditions of vaporload can be met with a single unit consisting of individual heatexchangers interconnected to a common cooling water source and a commonwater reservoir.

A further advantage of my invention is that I provide a simplifiedapparatus consisting of multiple heat exchange units of substantiallyidentical construction so that one or more can be temporarily removedfrom the system without seriously interfering with normal condensing andcooling operations.

A still further object of my invention is to provide a simplified.multiple unit condenser which has a high heat transfer efficiency yetwhich is relatively simple to construct and service and in which theoperating conditions are readily controlled.

Further objects and advantages of my invention will appear from thefollowing description of a preferred form of embodiment thereof taken inconnection with the attached drawing, in which:

Fig. 1 is an elevation view with parts in section of a heat exchangedevice for vapor condensation.

Fig. 2 is a plan view of the unit shown in Fig. 1.

In accordance with the preferred form of embodiment of my invention, theimproved heat exchange apparatus includes a plurailty of individual heatexchange units iii, the upper channels All of which are interconnectedto a common tank or drum I2 by lines 45. lhese heat exhange units areprimarily adapted to condense a vapor stream, which enters the heatexchangers as by manifold !3 with the resulting condensate removedtherefrom as by manifold M. Primarily, the heat exchange units asdisclosed are customary shell and tube type units which include a tubebundle 15, into the tubes of which a cooling medium is introduced as byheader or manifold H; in the space surrounding these tubes is thematerial (vapors) to be condensed.

The hot stream which is to be cooled is customarily a vapor although itwill be appreciated that it may be either a liquid such as a petroleumor a salt as used in the cooling of catalytic reaction chambers such asemployed in hydrocarbon cracking and the like or any other fluid. It isto be particularly noted, however, that the invention relates to thecooling of a hot stream as from a petroleum refinery, which stream ispassed through one or more of the heat exchange units l0 and which mustbe cooled in an efficient manner and which, if allowed to pass out ofthe heat exchange units without being cooled, will cause operatingdifiiculties. The cooling medium is generally water, and it will pass inindirect heat exchange relation with the hot stream in the heat exchangeunits.

I find that the individual heat exchange units are preferablyinterconnected in pairs to the common tank or drum I 2, and multiple hotstreams may be interconnected with the heat exchange units l6. It isdesirable to provide duplicate units from the standpoint of continuousoperation since cleaning can be accomplished by simply shutting off oneunit at a time and since no general shutdown is then required.Furthermore, in order to obtain flexibility of operation, I preferablyprovide valves 24 in vapor manifolds I 3 and valves 24a in condensatemanifolds M. In this manner, it is possible to conveniently vary thenumber of units In which may be required to take care of any particularhot stream. Similarly, I may also provide valves 25 and 25a to vary andcontrol the circulation of the cooling water through unit It].

One of the principal features of my invention, however, is the provisionof a reserve cooling water supply, which object is accomplished bymaintaining a volume of water in the drum l2, the latent heat value ofwhich is such that, if the inflow of cooling water ceases, it willrequire at least thirty minutes, for example, to bring about itsevaporation with the normal heating capacity of the hot streams. In theinterim, the flow of water through the tubes continues so that effectiveheat transfer takes place. This object may be accomplished by providingthe drum I2 in an elevated position and connecting it by downcomers 20with the bottom head 38 of heat of the heat exchange units l0 as throughthe header II, which serves to interconnect the bottom heads of theshell portions of the several heat exchange units.

The cooling water which enters the common header 4'! preferably underpressure passes through the branch pipes 39 to the respective heatexchange units [0 and passes through the tubes of the tube bundles l5 ofthe heat exchange units and discharges into the open reservoir l2. Thisreservoir has a drain pipe 42, through which theoverflow discharges towaste or external coolers. It will thus be seen that, under ordinaryservice, the flow of cooling water is once through the tubes of the heatexchange units with a resulting high rate of heat transfer. Inadvertentupward flow of the incoming cooling water through downcomers 20 isprevented by check valves 44. Each head 38 is provided with anindependent blow-down connection including valve 46, which is connectedto drains 41 or 41a respectively.

In accordance with my invention, under abnormal operation as during aninterruption in the water inflow through header l1, check valves 44open, and there is a continued circulation of water through the tubes ofunits I0 by virtue of the higher temperature of the water in the heatexchange tubes as compared with the temperature of the water in thedowncomers 20 and the tank l2. As the water slowly warms up because ofthe heat transfer in the condensing operation,

there will be some evaporation. With the evaporation of a part of thewater, however, the water level will gradually fall below the level ofthe connection 45 between the top of the heat exchange units and thetank. Until this condition occurs, the heat exchange rate issubstantially as high as it is with the once-through operation. Suchinitial abnormal operation, in which the temperature of the coolingwater is being raised to its boiling point, may be arranged to last forapproximately ten minutes under full load conditions. It is, of course,well known that the heat of evaporation of water is many times greaterthan the heat required to raise it to its boiling point.

If, in this time, it has not been possible to restore the water supplyor sufiiciently shutdown the unit, the reserve operation becomeseffective. In such case, the latent heat of evaporation of the entiresupply of water in the tank I2 is available to bring about the desiredcondensation.

It will be noted that the water will continue to flow from the tank [2through downcomersor return-flow conduits 20 into the lower partof therespective tube bundles of the condensing,

, enter the condensate trap 48 at the lower part of the unit.

For any predetermined operation, the amount of water in tank [2 can bepredetermined to give the desired safety factor. Ordinarily, stoppagesare of a temporary nature, and only a few minutes protection isrequired. My construction will adequately provide for this protection.If,

however, the refinery unit must be shut down, a time period of aboutthirty minutes is normally sufficient; and absolute safety for such atime is sible such economies of size and construction as to prove ofconsiderable benefit. The entire water supply can be at the desiredelevated height to assure adequate flow, and tank sizes can be l mitedto those found most effective for the operating conditions.

It will be apparent that, with water, it is usually preferable to havethe hot stream pass around the tubes in the shell as this mod ofoperation gives the highest heat transfer rate; but it will beunderstood that this feature also depends on the relative cleanness ofthe respective materials, and the reverse arrangement could be provided.

Although I have shown and described a preferred form of embodiment of myinvention, I am aware that modifications may be made thereto; and I,therefore, desire a broad interpretation of my invention within thescope and spirit of the description herein and of the claims appendedhereinafter.

I claim:

1. A heatexchange unit including a reservoir, shell and tube heatexchange means mounted adjacent the reservoir, means to introducecondensible hydrocarbon vapors into one end of the shell side of theheat exchange means,,means to remove the condensate therefrom, means tointroduce cooling water into one end of the tube side of the heatexchange mean in indirect contact with and countercurrent to the flow ofthe hydrocarbon vapors under a velocity to obtain a relatively high heattransfer rate, means to interconnect the other end of the tube side ofthe heat exchange means with the reservoir, said heat exchange meansbeing at such an elevation that the water, upon discharge therefrom,will fill th reservoir, means to maintain the normal level of water inthe reservoir above the upper end of the heat exchange tubes, saidreservoir being detached and at an elevation substantially equal to thetop of the heat exchange means, a returnfiow conduit between thereservoir and the water inlet end of the heat exchange means, and aselfactuating, normally closed valve in the returnflow conduit, saidvalve opening under thermosyphon action of the now of water upwardlythrough the heat exchange tubes from the reservoir when the supply ofcooling water is cut off, said reservoir maintaining a positive head ofliquid on said tubes irrespective of an external supply of coolingwater.

2. A condenser for hydrocarbon vapors, which comprises a reservoir, aplurality of detached individual vertical shell and tube heat exchangeunits, means to introduce cooling water under pressure to the lower endof the tubes of said units, means to connect the upper end of said tubeswith said reservoir whereby the water, after passing through said tubes,will fill said reservoir, said reservoir being elevated with respect tothe lower end of the heat exchange units, means attached to thereservoir to maintain the normal level of water in said reservoir abovethe top of said tubes, a vapor manifold interconnected to the upperportion of the shell side of said units for introduction of thehydrocarbon vapors in countercurrent, indirect heat exchange relationwith the cooling water, means to remove the condensate from the shells,a return-flow conduit from said reservoir interconnected to the lowerend of the tubes, a valve in said returnfiow conduit, said valve beingnormally closed to upward flow and automatically opening underthermosyphon action of the water flowing upwardly through said tube anddownwardly from said reservoir when the supply of pressure water to thetubes is cut off, said condenser having a heat transfer rate equal tothat of a shell and tube unit with the water in the tubes, and a safetyfactor of an available water supply equal to that of a typical submergedcondenser with the vapors in the tubes.

3. A condenser for vapors, which comprises an open tank, a shell andtube heat exchange unit mounted adjacent the tank, means to introducehydrocarbon vapors into one end of the heat exchange unit on the shellside thereof, means to remove the condensate therefrom, means tointroduce cooling water into the lower end of the tubes of the heatexchange unit in indirect conill tact with and countercurrent to theflow of the hydrocarbon vapors, said tubes being arranged in single passwith the upper end of said tubes being open, means to conduct theoverflow from saidtubes into the tank, means to maintain the normallevel of water in the tank above the upper end of the heat exchangetubes, said tank being elevated with respect to the lower end of thetubes, a return-flow conduit between the tank and the water inlet end'of the heat exchange tubes, and a self-actuating, normally closed valvein the return-flow conduit, said valve opening under the action of theflow of water from the tank into the tubes when the head of colder waterin the tank overbalances the head of warmer water in the tubes.

4. A condensing apparatus for condensing hydrocarbon vapors from adistillation process, which comprises at least two individual verticalshell and tube heat exchange units, means to introduce cooling waterunder pressure to the lower end of the tubes of said units, an elevatedand detached reservoir, means to interconnect the upper end of saidtubes with said reservoir whereby the water after passing through saidtubes will pass to said reservoir, means in said reservoir to maintainthe normal level of water in said reservoir above the top of said tubes,a vapor manifold interconnected to the upper portion of the shell sideof said units for introduction of the hydrocarbon vapor incountercurrent indirectheat exchange relation with the cooling water,means to remove the condensate from the shells, and a return-flowconduit extending from said reservoir to the lower part of the tubes insaid units whereby the Water in said reservoir will pass into said tubeswhen the supply of water under pressure to the tubes is cut off, saidcondenser having a heat transfer rate equal to that of a shell and tubeunit with the water in the tubes, said reservoir having an availablewater supply adequate to condense the vapors for a period substantiallyequivalent to that of a typical submerged condenser with the vapors inthe tubes.

5. A condensing apparatus for independently condensing at least twoindependent streams of hydrocarbon vapors from a distillation process,which comprises at least four individual vertical shell and tube heatexchange units, means to introduce cooling water under pressure to thelower end of the tubes in' said units, the upper end of said tubes beingopen, an elevated and detached reservoir, means to connect the open endof said tubes with said reservoir whereby the water after passingthrough said tubes will pass into said reservoir, means in saidreservoir to maintain the normal level of water in said reservoir abovethe top of said tubes, vapor manifolds interconnected to the upperportion of the shell side of each pair of said units for introduction ofthe separate streams of hydrocarbon vapors in countercurrent indirectheat exchange relation with the cooling water, valves in each of saidvapor manifolds whereby the independent vapor streams may be introducedinto one or more of the respective units, a condensate manifoldinterconnected to said shells for the removal of condensate therefrom,and return-flow conduit extending from said reservoir to the lowerportion of said tubes whereby the water from said reservoir will flowinto the lower end of said tubes and by thermosyphon action will flowupwardly through said tubes into said reservoir when the supply ofpressure water to the tubes is out 01f,

said condenser having a heat transfer rate equal to that of a shell andtube unit with the water in the tubes, and a safety factor of anavailable water supply equal to that of a typical submerged condenserWith the vapors in the tubes.

6. An apparatus for use with conventional petroleum distillationequipment of the type wherein a plurality of independent streams of hotoil is removed therefrom and cooled, the combination therewith of a heatexchanger consisting of 10 at least four identical interconnected unitsof the shell and tube type, a common elevated and detached water drum,means for introducing water into said units, means to discharge waterinto CERTIFICATE OF CORRECTION. Patent No. 2 ,Lgm. July 6, 19M.

WHEATON N. KRAFT.

It is hereby certified that error appears in the printed p cification ofthe above numbered patent requiring correction as follows; Page 2, firstcolumn, line 59, for "heat" first occurrence, read each--; and that thesaid Letters Patent should be read with this correction therein that thesame may conform to the record of the case in the Patent Office Signedand sealed this 10th day of August, A. D. 194.5

Henry Van Arsdale, (Seal) Acting; Commissioner of Patents.

